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At the end of the Pluto tour we spent some time watching a movie in the
3-D digital theatre where we learned more about the 100 years of
celestial research on Mars Hill then joined another group for the Mars
tour. This tour included a visit to the historic Rotunda Library where
we saw some of the original astronomical research tools.

Displays include the Millionaire, one of the earliest motorized
calculating machines, used at the Lowell Observatory from about 1914 to
the early 1930s. Percival Lowell’s assistants, known as ‘computers’ at
the time, devoted seven years to making mathematical calculations to
test different astronomical projections that led to the discovery of
Pluto. Work done on that early machine could be completed today in a
matter of hours by today’s computers using high-speed microprocessors.
A display cabinet in the Rotunda Library shows several historic
instruments used in early astronomical research. On one of the shelves
is a 1920s Clock Drive used to regulate the motion of a telescope as it
tracks the stars and planets during the course of the night. On another
shelf is Thacher’s Calculating Instrument, a slide rule commonly used
many years ago to make rapid mathematical calculations. Much larger than
the typical ten inch scale slide rule, the Thacher slide rule unfolds
to a mighty sixty feet in length thus significantly increasing the
accuracy needed for astronomical data analysis.

Also among the displayed antique items was a Radiometer. When light from
a star or small area of a planet was focused on the sensor of the
Radiometer, astronomers could use the generated minute electric current
to estimate the radiation and temperature of the far away objects. Along
with these and numerous other items used in the Observatory’s
pioneering research, the Rotunda Library contains volumes of priceless
books on astronomical theories and research.

The Mars tour also stops at the Clark Dome just up the hill from the
Rotunda Library. Inside the Dome is the 24-inch refracting Alvan Clark
Telescope, purchased for 24 thousand dollars in 1909 but would cost more
than 70 billion dollars today. To track celestial targets, the massive
11-ton telescope projects through an opening in the dome’s roof and can
be rotated into position with the assistance of automobile tires.
Sitting on an elevated platform is the chair used by Percival Lowell
during his many hours of watching the heavenly bodies.

At one time the Clark Dome also provided ideal climatic shelter for
thermometers, hygrometers (to monitor humidity) and other weather
station instrumentation used to understand and predict weather patterns
necessary in planning successful observations. That instrumentation was
removed in the latter part of the 20th century and replaced with a
modern weather station located on top of the Clark Dome. Nearby on a
shady hillside facing Mount San Francisco is the mausoleum containing
the remains of Percival Lowell who died on November 12, 1916.
Everything that we heard and saw during the tours and the movie set the
stage for observing the night sky as we’d never seen it before.

The red
landscape lighting along the center’s pathways focuses downward and
visitors were asked not to use flash photography to ensure that our
pupils were fully open when it was our turn at the telescope. With the
assistance of our guide, each of us climbed the short step ladder and
peered expectantly through the telescope’s eyepiece. There was a long
line so each of us had less than a minute to view the craters on the
edge of the nearly full moon; craters created eons ago by the impact of
asteroids. Awesome, cool, wow and other superlatives were expressed by
young and older alike. When everyone had seen the moon up close, the
guide located Saturn, focused the telescope then invited each of us to
climb the ladder again to view the rings around Saturn. It was
fantastic, much better than any picture I’d ever seen.

Each year more than 80,000 visitors find their way up Mars Hill to the
Lowell Observatory. I’m sure that, like me, most of them leave with a
profound respect for the work led by Percival Lowell and his staff of
astronomers to document the wonders of outer space.

The Observatory is funded with donations from private sources. It was
designated a Registered National Historic Landmark by the US Department
of Interior National Park Service in 1966. Admission fees are $8 for
adults, $7 for seniors, AAA members and college students; $4 children
(ages 5 – 17). If you come during the daytime, simply show your receipt
for reentry for the evening program.